<!doctype html>
<html>

<head>
  <meta charset="utf-8">
  <title>Canvas模拟火焰演示</title>

  <style>
    @import url(https://fonts.googleapis.com/css?family=Amatic+SC);

    html,
    body {
      margin: 0;
      padding: 0;
      height: 100%;
    }
  </style>

</head>

<body>
  <canvas id="zjcopy"></canvas>

  <script>
    var Fire = function () {

      this.canvas = document.getElementById('zjcopy');
      this.ctx = this.canvas.getContext('2d');
      this.canvas.height = window.innerHeight;
      this.canvas.width = window.innerWidth;

      this.aFires = [];
      this.aSpark = [];
      this.aSpark2 = [];



      this.mouse = {
        x: this.canvas.width * .5,
        y: this.canvas.height * .75,
      }



      this.init();

    }
    Fire.prototype.init = function () {

      this.canvas.addEventListener('mousemove', this.updateMouse.bind(this), false);

    }
    Fire.prototype.run = function () {

      this.update();
      this.draw();

      if (this.bRuning)
        requestAnimationFrame(this.run.bind(this));

    }
    Fire.prototype.start = function () {

      this.bRuning = true;
      this.run();

    }
    Fire.prototype.stop = function () {

      this.bRuning = false;

    }
    Fire.prototype.update = function () {

      this.aFires.push(new Flame(this.mouse));
      this.aSpark.push(new Spark(this.mouse));
      this.aSpark2.push(new Spark(this.mouse));



      for (var i = this.aFires.length - 1; i >= 0; i--) {

        if (this.aFires[i].alive)
          this.aFires[i].update();
        else
          this.aFires.splice(i, 1);

      }

      for (var i = this.aSpark.length - 1; i >= 0; i--) {

        if (this.aSpark[i].alive)
          this.aSpark[i].update();
        else
          this.aSpark.splice(i, 1);

      }


      for (var i = this.aSpark2.length - 1; i >= 0; i--) {

        if (this.aSpark2[i].alive)
          this.aSpark2[i].update();
        else
          this.aSpark2.splice(i, 1);

      }

    }

    Fire.prototype.draw = function () {

      this.ctx.globalCompositeOperation = "source-over";
      this.ctx.fillStyle = "rgba( 15, 5, 2, 1 )";
      this.ctx.fillRect(0, 0, window.innerWidth, window.innerHeight);

      this.grd = this.ctx.createRadialGradient(this.mouse.x, this.mouse.y - 200, 200, this.mouse.x, this.mouse.y - 100, 0);
      this.grd.addColorStop(0, "rgb( 15, 5, 2 )");
      this.grd.addColorStop(1, "rgb( 30, 10, 2 )");
      this.ctx.beginPath();
      this.ctx.arc(this.mouse.x, this.mouse.y - 100, 200, 0, 2 * Math.PI);
      this.ctx.fillStyle = this.grd;
      this.ctx.fill();


      this.ctx.font = "15em Amatic SC";
      this.ctx.textAlign = "center";
      this.ctx.strokeStyle = "rgb(50, 20, 0)";
      this.ctx.fillStyle = "rgb(120, 10, 0)";
      this.ctx.lineWidth = 2;
      this.ctx.strokeText("Fire", this.canvas.width / 2, this.canvas.height * .72);
      this.ctx.fillText("Fire", this.canvas.width / 2, this.canvas.height * .72);



      this.ctx.globalCompositeOperation = "overlay";//or lighter or soft-light

      for (var i = this.aFires.length - 1; i >= 0; i--) {

        this.aFires[i].draw(this.ctx);

      }

      this.ctx.globalCompositeOperation = "soft-light";//"soft-light";//"color-dodge";

      for (var i = this.aSpark.length - 1; i >= 0; i--) {

        if ((i % 2) === 0)
          this.aSpark[i].draw(this.ctx);

      }


      this.ctx.globalCompositeOperation = "color-dodge";//"soft-light";//"color-dodge";

      for (var i = this.aSpark2.length - 1; i >= 0; i--) {

        this.aSpark2[i].draw(this.ctx);

      }


    }

    Fire.prototype.updateMouse = function (e) {

      this.mouse.x = e.clientX;
      this.mouse.y = e.clientY;

      //this.aFires.push( new Flame( this.mouse ) );

    }








    var Flame = function (mouse) {

      this.cx = mouse.x;
      this.cy = mouse.y;
      this.x = rand(this.cx - 25, this.cx + 25);
      this.y = rand(this.cy - 5, this.cy + 5);
      this.vy = rand(1, 3);
      this.vx = rand(-1, 1);
      this.r = rand(20, 30);
      this.life = rand(3, 6);
      this.alive = true;
      this.c = {

        h: Math.floor(rand(2, 40)),
        s: 100,
        l: rand(80, 100),
        a: 0,
        ta: rand(0.8, 0.9)

      }


    }
    Flame.prototype.update = function () {

      this.y -= this.vy;
      this.vy += 0.05;


      this.x += this.vx;

      if (this.x < this.cx)
        this.vx += 0.1;
      else
        this.vx -= 0.1;




      if (this.r > 0)
        this.r -= 0.1;

      if (this.r <= 0)
        this.r = 0;



      this.life -= 0.15;

      if (this.life <= 0) {

        this.c.a -= 0.05;

        if (this.c.a <= 0)
          this.alive = false;

      } else if (this.life > 0 && this.c.a < this.c.ta) {

        this.c.a += .08;

      }

    }
    Flame.prototype.draw = function (ctx) {

      ctx.beginPath();
      ctx.arc(this.x, this.y, this.r * 3, 0, 2 * Math.PI);
      ctx.fillStyle = "hsla( " + this.c.h + ", " + this.c.s + "%, " + this.c.l + "%, " + (this.c.a / 20) + ")";
      ctx.fill();

      ctx.beginPath();
      ctx.arc(this.x, this.y, this.r, 0, 2 * Math.PI);
      ctx.fillStyle = "hsla( " + this.c.h + ", " + this.c.s + "%, " + this.c.l + "%, " + this.c.a + ")";
      ctx.fill();

    }








    var Spark = function (mouse) {

      this.cx = mouse.x;
      this.cy = mouse.y;
      this.x = rand(this.cx - 40, this.cx + 40);
      this.y = rand(this.cy, this.cy + 5);
      this.lx = this.x;
      this.ly = this.y;
      this.vy = rand(1, 3);
      this.vx = rand(-4, 4);
      this.r = rand(0, 1);
      this.life = rand(4, 5);
      this.alive = true;
      this.c = {

        h: Math.floor(rand(2, 40)),
        s: 100,
        l: rand(40, 100),
        a: rand(0.8, 0.9)

      }

    }
    Spark.prototype.update = function () {

      this.lx = this.x;
      this.ly = this.y;

      this.y -= this.vy;
      this.x += this.vx;

      if (this.x < this.cx)
        this.vx += 0.2;
      else
        this.vx -= 0.2;

      this.vy += 0.08;
      this.life -= 0.1;

      if (this.life <= 0) {

        this.c.a -= 0.05;

        if (this.c.a <= 0)
          this.alive = false;

      }

    }
    Spark.prototype.draw = function (ctx) {

      ctx.beginPath();
      ctx.moveTo(this.lx, this.ly);
      ctx.lineTo(this.x, this.y);
      ctx.strokeStyle = "hsla( " + this.c.h + ", " + this.c.s + "%, " + this.c.l + "%, " + (this.c.a / 2) + ")";
      ctx.lineWidth = this.r * 2;
      ctx.lineCap = 'round';
      ctx.stroke();
      ctx.closePath();

      ctx.beginPath();
      ctx.moveTo(this.lx, this.ly);
      ctx.lineTo(this.x, this.y);
      ctx.strokeStyle = "hsla( " + this.c.h + ", " + this.c.s + "%, " + this.c.l + "%, " + this.c.a + ")";
      ctx.lineWidth = this.r;
      ctx.stroke();
      ctx.closePath();

    }

    rand = function (min, max) { return Math.random() * (max - min) + min; };
    onresize = function () { oCanvas.canvas.width = window.innerWidth; oCanvas.canvas.height = window.innerHeight; };



    var oCanvas;
    init = function () {

      oCanvas = new Fire();
      oCanvas.start();

    }


    window.onload = init;
  </script>

</body>

</html>